<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>计算年龄案例</title>
    <SCRipt>
        var year= prompt('请输入您的出生年份')
        var age = 2021 - year 
        alert('你今年已经' + age + '岁了')
    </SCRipt>
</head>
<body>
    
</body>
</html>